1. Field of the Invention
The present invention relates to an image processor, an image processing method and an image processing program, and more particularly to an image processor, an image processing method and an image processing program for generating image regeneration output data having accurate density characteristics and high grayscale characteristics, even for low bit image regeneration output data.
2. Description of the Related Art
An image processor used for such an image formation device as a printer and copier converts the grayscale input data of pixels into the image regeneration output data corresponding to the dot size in the pixels by half tone processing. The grayscale input data is 8 bit grayscale value data, for example, and is data having 256 grayscales between the minimum value (0% grayscale value) to the maximum value (100% grayscale value). Such grayscale input data is converted into the output data with the size of the dots formed in a pixel by a multi-value dither method. If the output data has 8 bits, the dot size in the pixel has 256 grayscales. And this output data is supplied to the print engine, and based on the supplied output data, the print engine forms dots in the pixels. Such image regeneration output data corresponds to the beam width data of the laser beam to be irradiated onto the image drum, or the pulse width data for driving the laser, for example, in the case of the electro-photography scanned by the laser beam.
According to general half tone processing, the grayscale input data is converted into the output data for image regeneration (pulse width data) by referring to a gamma table storing the output data corresponding to the grayscale input data. And based on this output data, the pulse width modulation unit generates drive pulse signals of the laser and supplies them to the print engine. By appropriately designing this gamma table, a desired screen can be provided using the output data for image regeneration. The screen characteristics includes the screen line count, for example.
Image processing involving such half tone processing is stated in Japanese Patent Application Laid-Open No. 2000-85187 and Japanese Patent Application Laid-Open No. 2000-228728, for example.
In conventional half tone processing, 8-bit grayscale input data, for example, is converted into output data with 8 or less bits, and the dot size in pixels is determined by this output data. Therefore the dot size in pixels generated as an image has the number of grayscales corresponding to the number of bits of the output data, and it is preferable to increase the number of bits of the output data in order to increase the number of grayscales.